JPS6367186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for developing a latent image with a developer, and more specifically, it uses a magnetic developer (hereinafter referred to as magnetic toner) to develop a latent image on a developer support. The present invention relates to a latent image developing device that develops an image area of an electrostatic image holding means by adjusting the thickness so that a developer layer does not come into contact with a non-image area of the electrostatic image holding means at least in a developing section.

Conventionally, methods employed in developing devices for electrophotography and electrostatic recording are broadly classified into dry developing methods and wet developing methods. The former method is further divided into methods using a two-component developer and methods using a single-component developer. Two-component developing methods include, depending on the type of carrier used to transport the toner, a magnetic brush method using an iron powder carrier, a cascade method using beads and carriers,
There is a fur brush method using fur, etc. Furthermore, the one-component development methods include the powder cloud method, in which toner particles are sprayed, and the contact development method, in which toner particles are brought into direct contact with the electrostatic latent image surface. (also referred to as toner development), jumping development method in which toner particles are not brought into direct contact with the electrostatic latent image surface, but are charged and flown toward the latent image surface by the electric field of the electrostatic latent image; magnetic conduction There is the MagneDry method, which develops by bringing a toner into contact with the electrostatic latent image surface.

Two-component development methods inevitably use a developer mixture of carrier particles and toner particles, and as the development process normally progresses, toner particles are consumed in far larger quantities than carrier particles, so the mixing ratio of the two changes. However, they inherently have drawbacks such as fluctuations in the density of the visible image and deterioration of image quality due to deterioration of carrier particles that are difficult to consume due to long-term use.

On the other hand, in one-component developing methods, the Magne-Dry method using magnetic toner and the contact developing method without magnetic toner, the toner contacts the entire surface of the surface to be developed, that is, both the image area and the non-image area. However, there was a problem in that the toner easily adhered to non-image areas, resulting in so-called background fog, which was easily smudged (this fog smudge was also a drawback in two-component developing methods). . Further, even in the powder cloud method, it is inevitable that powdered toner particles adhere to non-image areas, and the method also has the disadvantage that background fog cannot be removed.

Furthermore, in the so-called jumping development method, which belongs to the one-component development method, toner is uniformly applied to a carrier such as a sheet, and then the toner is opposed to an electrostatic image holding surface with a small gap, so that the electrostatic charge is removed from the toner carrier. A method is known in which toner is attracted and adhered to the image holding surface by the electric charge of the electrostatic image (Japanese Patent Publication No. 1973-
9475, US Pat. No. 2,839,400, etc.). This method has the advantage that not only the toner is not attracted to the non-image area where there is no static charge, but also the toner and the non-image area do not come into contact with each other, so that the above-mentioned fogging is less likely to occur. In addition, since carrier particles are not used, there is no variation in the mixing ratio as described above.
Furthermore, there is no deterioration of carrier particles.

However, this method has the following drawbacks, which hinder its practical application.

Practical uniform application is difficult. Although an electric field is applied to the toner carrier sheet in advance to make the toner adhere to the toner carrier sheet, it is difficult to obtain uniform adhesion.

As a method for uniformly applying toner, a well-known rigid blade is used. However, unlike liquid toner, it is difficult to apply particles uniformly and thinly, and uneven application tends to occur. Since this unevenness is directly reproduced during development, it is not suitable for practical image reproduction. One way to improve this problem is to use cloth, paper, etc. as the surface of the sheet that carries the toner, and embed the toner into the fibers, but this makes it difficult to create fine-grained toner particles due to the roughness of the fibers, making it difficult to apply uniformly. It's hard to say it's possible.

On the other hand, the cascade development method in which toner is applied to a sheet-like carrier in advance requires a large-sized apparatus, which is also impractical.

It is an object of the present invention to eliminate these conventional drawbacks and provide a high-quality latent plaster device. Specifically, the present invention provides: (1) A uniform toner layer is obtained using a simple device.

(2) Maintain an extremely thin toner layer with uniform layer thickness and density in the developing section.

The purpose is to

The present invention is a developing device that achieves the above object, and includes a moving developer support means provided opposite to an electrostatic image holding means, and a thickness of a magnetic developer layer formed on the developer support means. fixed magnetic field generating means for regulating the distance between the developer supporting means and the electrostatic image holding means to be less than or equal to the distance q; and a developing device provided at the developer supporting means with a distance p in the magnetic field of the fixed magnetic field generating means. a thickness regulating means for the developer layer, the regulating means is made of a magnetic material or a magnet, and a distance p with respect to the developer supporting means is equal to or less than a distance q between the latent image holding means and the developer supporting means. characterized by something.

Embodiments of the apparatus according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic configuration of an example of a copying device or a recording device to which a developing device according to the present invention can be applied. Of course, it is not limited to this.

Reference numeral 1 denotes a photosensitive drum including a photoconductive layer, and either one with or without an insulating layer on the surface can be used, and of course, a sheet-shaped or belt-shaped one is also possible. Reference numeral 2 represents a known photosensitive charging device, and 3 represents a light image irradiation device that projects an original image, a light image, or a light beam modulated by an image signal. An electrostatic image is formed on the photoreceptor 1 by these. This electrostatic image forming process is the so-called Carlson process, or Japanese Patent Publication No. 42-23910, No. 43-24748,
The processes described in 42-19748, 44-13437, etc., and other processes can be applied. 4
1 is a developing device according to the present invention, which forms a toner particle visual image in accordance with the electrostatic image on the photoreceptor 1. 5 is a device for transferring the toner image onto a transfer material 6. Incidentally, in order to improve the transferability, the visible image may be charged in advance by corona discharge or the like before transfer. It is also possible to adopt a so-called electrostatic image transfer method in which the electrostatic image on the photoreceptor 1 is temporarily transferred to another image carrier and then converted into a visible image by the developing device 4. Reference numeral 7 denotes a cleaning device for cleaning and removing residual toner on the photoreceptor 1 after transfer, and for reusing the photoreceptor.

FIG. 2 shows an embodiment of the developing device according to the present invention. In the figure, numeral 1 denotes a photosensitive drum as an electrostatic image holding means, which may of course be in the form of a belt or sheet. Reference numeral 8 denotes developer supporting means provided opposite to this holding means, and the one shown is a non-magnetic cylinder. Reference numeral 9 denotes a magnetic roll fixedly installed within the cylinder, which has at least a magnetic pole for pumping the developer onto the cylinder, further has a developing magnetic pole at the developing position, and has a developer transporting magnetic pole between them. Have it as appropriate. Reference numeral 10 denotes a doctor blade made of a magnetic material or a magnet that regulates the thickness of the insulating magnetic toner 12 thus supplied to the cylinder. (hereinafter referred to as Doctor Blade)
The thickness of the toner layer 11 is regulated by the distance between the doctor blade 10 and a non-magnetic cylinder surrounding the magnet roll 9 (hereinafter also referred to as a sleeve). usually,
The toner layer is regulated in the range of 30μ to 300μ. In a magnetic field, magnetic toner forms a string along the lines of magnetic force, and its density is significantly lower than in a normal state. Therefore, if the toner thickness is controlled with a doctor blade in the magnetic field, it can be controlled to be much thinner than in the area where the magnetic field does not reach. If a blade is used to regulate the toner in areas where the magnetic field does not reach, the distance between the doctor blade 10 and the toner support means 8 must be made very small, which is mechanically difficult and difficult to obtain a uniform toner layer.

The effect of the magnet 9 can be recognized as long as the doctor blade 10 is within the range covered by the magnetic field due to the magnetic pole of the magnet, but especially when the magnetic pole faces the doctor blade 10, the toner layer can be regulated to be extremely thin. If the doctor blade 10 is a magnetic material,
The magnetic field is concentrated on the doctor blade, and the brush-like toner is arranged like a curtain between the toner support means and the doctor blade, thereby preventing the toner from passing through. The toner slightly dragged by the toner support means 8 only passes through a small amount along the surface of the toner support means. Therefore, the toner layer 11
can be made extremely thin as described above. If a magnet is used as the doctor blade 10, the magnetic field in that part will be even stronger and more effective.

In this way, when a magnetic material or a magnet is used as the doctor blade 10, the thickness of the toner layer that passes through the blade 10 along the surface of the toner support means is thinner than the distance from the doctor blade.

FIG. 3 shows experimentally obtained data on the relationship between the distance between the doctor blade and the toner support and the toner thickness at the magnetic pole position. As an example, using three types of insulating one-component magnetic toner, the toner layer thickness at the magnetic pole position on the toner support means (y
axis).

As an electrically insulating and magnetic toner, (a)
55 parts of polyester, 20 parts of magnetite, 2 parts of carbon, 2 parts of charge control agent with external addition of 0.1% colloidal silica, (b) 50 parts of polystyrene, 40 parts of magnetite, 3 parts of charge control agent, 6 parts of carbon
A mixture containing 0.1% colloidal silica externally added, (c) 50 parts polystyrene, 40 parts magnetite, 3 parts charge control agent, and 6 parts carbon was used. Further, the magnetic pole of the magnet was arranged at the closest portion between the electrostatic image holding member and the toner carrier, and the surface magnetic flux density at that time was set to 800 Gauss.

As can be seen from this, it is generally recognized that when the gap P between the doctor blade 10 and the toner support 8 is in the range of approximately 50 to 200 μ, the toner layer thickness increases as the gap increases. On the other hand, when the gap is in the range of about 200 to 450 μ, the toner layer thickness does not increase to the extent that the gap increases, but remains the same or increases slightly. It can also be seen that the toner layer thickness itself (at the magnetic pole position) is always formed thinner than the above-mentioned gap.

Although not shown in the graph of FIG. 3, even if a small amount of uneven coating of the developer layer on the surface of the toner support occurs, the doctor blade and toner support are within a range that can be practically used during development. It was found that the value of the distance P from the surface can be up to about 800μ. If it exceeds 800μ, the magnetic force acting on this distance P weakens, making it impossible to provide a uniform coating to the extent necessary for development, causing unevenness in the toner layer, which appears as image unevenness.

If the distance P is less than 100 microns, the toner layer will have a thickness of several tens of microns to several tens of microns, making it impossible to obtain a sufficient image density.

The thickness t of the toner layer is 1/5 to less than 1/1 of the gap P (1/5P≦t<1/1P) because the toner layer is coated due to the magnetic binding force at the above-mentioned gap P. This varies depending on the toner material, the magnetic flux density of the interval P, the shape of the blade, etc., but the larger the magnetic force, the smaller the toner layer thickness. becomes thinner.

When the gap q between the latent image carrier and the toner support is smaller than the toner layer thickness, the toner layer is pressed against the latent image carrier, which is usually a photoconductor, and not only does toner force aggregation occur, but the photoconductor, etc. cause damage. If the thickness is 10 times or more than the thickness of the toner layer, the toner will not reach the photoreceptor sufficiently, resulting in not only low image density but also extremely thin line copies, and in some cases even broken lines. This is thought to occur because the lines of electric force from the photoreceptor do not sufficiently reach the toner support, but instead are directed toward the periphery of the line.

Even if the distance P between the doctor blade and the toner support means is longer than the distance q between the electrostatic image support means and the toner support means (P > q), the thickness of the toner standing up on the toner support means can be reduced by the electrostatic image retention means in the developing section. It is generally possible to regulate the thickness so that the toner does not come into contact with the non-image areas of the toner. However, when toner, paper powder, etc. aggregated in the toner layer on the toner support means accumulate in the thickness regulation section using the doctor blade, the thickness regulation using the doctor blade is not performed effectively, and the distance between the doctor blade and the toner support means is close to It may occur that a thick toner layer is conveyed along the surface of the toner support means to the development station.

At this time, the aggregated toner is compressed between the electrostatic image holding means and the toner supporting means, which may adversely affect the image, and paper dust, chips, etc. may damage the electrostatic image holding means. In order to prevent this, it is necessary that the distance P between the doctor blade and the toner support means is at least not wider than the distance q between the electrostatic image holding means and the toner support means. That is, it is necessary to satisfy P≦q. As mentioned above, q is larger than the toner layer thickness and is preferably set at a small interval equal to 10 times the thickness, but numerically, q is 100μ.
It is preferable that ≦q≦900μ.

In the present invention, the doctor blader 10 can have the two effects of regulating the thickness of the toner layer and preventing agglomeration of toner as preferable effects, and the apparatus can be simplified.

The composition and material of each element commonly used in the above embodiments will be explained here.

First, as an example of magnetic toner, 50 parts of polystyrene, 40 parts of magnetite, 3 parts of charge control agent,
Of course, a well-known magnetic toner formed by mixing 6 parts of carbon can be used. As the toner support, an aluminum material is used as a non-magnetic material, and it is formed into a hollow cylindrical shape as shown in the figure, so that the toner outermost layer supported thereon has substantially the same speed in the same direction as the electrostatic image holding member. As an example
It was driven at 100mm/sec. The magnet has a magnetic pole located closest to the electrostatic image (potential contrast approximately 600V) holding member and toner carrier, and the surface magnetic flux density at that time is within the range of approximately 600 to 1300 Gauss.
I chose 800 Gauss. The doctor blade is an example of a magnetic material, which is installed at the magnetic pole position of an iron blade and a magnet, and the distance between the doctor blade and the toner carrier is set to 250μ, and the distance between the toner carrier and the electrostatic image holder is set to 300μ. It was possible to obtain a microscopic image of excellent image quality with no stains caused by aggregated toner or background fog on the electrostatic image holding surface.

Incidentally, this is a device in which conductive toner is attached to the outer peripheral surface of a fixed sleeve having a rotating magnet roll by the magnetic force of the magnet roll, and the toner is transported and developed by rotating the magnet roll. , an apparatus is proposed in which a magnetic body is placed opposite to the outer circumferential surface of the sleeve, and the layer thickness of the toner adhering to the outer circumferential surface of the sleeve is regulated by the magnetic force generated by the magnet roll and the magnetic body. (Japanese Unexamined Patent Publication No. 125844/1983). However, in the device described in this publication, the thickness of the toner layer on the sleeve is regulated by the magnetic material so that it is thicker than the developing gap between the sleeve and the latent image carrier, and the toner surface layer is inevitably thicker than the developing gap between the sleeve and the latent image carrier. Requirements include that it easily adheres to non-image areas, and that the sleeve is fixed and the magnet inside it is rotated to vary the magnetic field that acts between the opposing magnetic body. be.

However, the embodiment according to the present invention has elements different from each of these elements as described in detail above, and in particular, a developer thickness regulating means and a developer layer are provided for regulating the developer layer thickness. It has a means for maintaining the distance P between the support member and the distance P at least not larger than the distance q between the latent image holding means and the developer support means (P≦q), so that the thickness of the developer is thinner than the distance P. It is possible to obtain a layer with uniform density, uniform density, and uniform thickness at the same time, and uniform development can be performed.

The present invention is not limited to the above embodiments, but includes various embodiments that are conceptually included.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a device to which the developing device according to the present invention can be applied, and FIG. 2 is a sectional view of a developing device according to the present invention.
FIG. 3, which is a cross-sectional view of the embodiment, is a graph showing the change in toner layer thickness with respect to the change in the distance P between the doctor blade and the toner support. 1...Latent image holding means, 8...Developer supporting means, 9...
Magnetic field generating means, 10... means for regulating the thickness of the developer.

Claims (1)

[Claims] 1. A movable developer support means provided opposite to the electrostatic image holding means, and a thickness of a magnetic developer layer formed on the developer support means. Fixed magnetic field generating means for regulating the distance from the electrostatic image holding means to q or less, and thickness regulating means for the developer layer provided on the developer supporting means at a distance p in the magnetic field of the fixed magnetic field generating means. , wherein the regulating means is made of a magnetic material or a magnet, and a distance p to the developer supporting means is equal to or less than a distance q between the latent image holding means and the developer supporting means. Device. 2. The developing device according to claim 1, wherein the distance p is within a range of 100μ to 800μ, and the distance q is within a range of 100μ to 900μ. 3. The developing device according to claim 1, wherein the regulating means faces a magnetic pole of the fixed magnetic field generating means.